/Engine/Source/Runtime/MeshDescription/Public/MeshDescription.h
Deletes triangles from the mesh and remove all orphaned polygon groups, vertex instances, edges and vertices. Will not compact the internal arrays, you must callCompact()manually.
void DeleteTriangles ( const [TArray](API\Runtime\Core\Containers\TArray)< [FTriangleID](API\Runtime\MeshDescription\FTriangleID) > & Triangles )